I posted this up at E90post but got no love, so I'm here hoping M3 enthusiasts will be keener to answer

I'd like to upgrade the bushings on my car. I plan to get these changed at 30k miles, which I've heard is the time when things start going...

I'm running a 335i E90 LCI. Car is a DD, so it needs to be streetable...

What I'm in for:
Front Lower Control Arm Bushings (LCAB) - Motorsport Race
- I guess this is a no-brainer, at the price? $99

Rear subframe
My biggest dilemma. I've heard of the E46 subframe cracking, and I'm scared that this would happen on my car if I switched to solids?
On the other hand, some people say that by going solid you actually reduce the risk of cracking the shell/subframe? I don't understand this... the bushings damp any forces acting on the subframe and prevent them from reaching the body shell. If you remove the rubber and put in solids, then there is nothing to damp the forces and ALL of it is transmitted into the shell?
Sooo... options are stock M3 subframe bushings, or Turner Delrin, or polyurethane...

Is there anything else that needs doing at around 30k bushing wise? Any NVH associated with these mods?

Also, is it good to do anything else while getting the subframe bushings changed? I've heard its wise to do the rear sway bar? How will the car handle provided that I only switch the rear sway and keep the front sway OEM (M packet)?

Harder rubber will add some NVH. But why go to such lengths to change these bushings out? Are they bad? If I were dropping the subframe for some reason, sure. But I wouldn't just do it to do it. The E46 had known issues with the FCAB, RTABs, and either the diff monts or the subframe bushings (one would go, the other would be OK). I'm not aware of any issues with the E9X platform.

I also think the E9X M3 suspension design is more durable than the E46 design.

I did them all in my 1 series and was happy with them. It's quite an investment of both time and money to get them installed, but it does transform the car. Really they only require replacement as an upgrade, not because they are worn. If your car has additional power, it is worth it. If you're a track junkie, it is worth it. Otherwise leave them alone as it will be a waste of money. The additional torque from even just software over works the rear suspension and the car cannot track straight. Just know that once you start to upgrade the parts, it never stops. The easiest and best way to upgrade them is to buy an M3. Trust me on that one!

One of the most popular initial suspension mods for the E9x car is to replace the front lower contorl arms with pieces from the E9x M3. The M3 parts have stiffer and better bushings plus they are slightly longer helping you achieve a little more negative camber. In most peoples mind this is a much better mod than simply replacing the bushings.

The rear subframe bushings are soft and are typically replaced with M3 bushings but this is fairly labor intensive involving dropping the subframe 6 inches or so to gain clearance for the bearing press. Probably not neccesary if you're not going to upgrade the shocks and springs.

I wouldn't replace the rear swaybar unless you were doing a complete sport suspension install. Do the springs and shocks before the swaybars; they make the biggest difference.

On my old 135i, I did the M3 front parts and the rear M3 subframe bushings (all done myself) and the rear was more noticeable than the front. It is the same rear carrier in the E82 to the E9X, so it's the same job to replace the rear bushings. Not for the faint of heart, and suggest sourcing the proper bushing press, if you are doing it yourself. I made mine, and it was harrowing.

You didn't mention if you track your car, but you did mention that the roads are bad where you are. These modifications you are contemplating will stiffen the ride. So unless you are tracking the car, stick to OEM - or the M3 parts.